President Obama on Tuesday moved to preserve more than 1,600 acres of coastal land in Northern California by declaring them part of a national monument. Point Arena-Stornetta, a 12-mile stretch of coast made up of federal and state public lands, is about 140 miles north of San Francisco. It will now be part of the California Coastal National Monument, a marine boundary that includes islands, rocks and reefs owned by the United States and within 12 miles of California’s 1,100-mile coast. Point Arena-Stornetta is the first shoreline portion of the monument. “It is a place where scientists do research; where people who just want to experience the great outdoors can take advantage of it,” Mr. Obama said before signing the proclamation. The newly expanded coastal monument is home to a variety of fauna and flora, among them Steller sea lions, Behren’s silverspot butterfly, rare bird species like the black oystercatcher, and a bishop pine forest.